#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<vector>
using namespace std;

class Solution {
public:
    int tribonacci(int n) {
        vector<int> v;
        v.push_back(0);
        v.push_back(1);
        v.push_back(1);
        v.resize(n + 1);
        int i = 3;
        for (i = 3; i <= n; i++)
        {
            v[i] = v[i - 1] + v[i - 2] + v[i - 3];
        }
        return v[n];
    }
};
class Solution {
public:
    int tribonacci(int n) {
        if (n == 0)
        {
            return 0;
        }
        if (n == 1 || n == 2)
        {
            return 1;
        }
        int a = 0;
        int b = 1;
        int c = 1;
        int d = 0;
        for (int i = 3; i <= n; i++)
        {
            d = a + b + c;
            a = b;
            b = c;
            c = d;
        }
        return d;
    }
};